The administrator at the current moment is just a device for Fujino to use to explain away certain shenanigans, and be used as a constantly updating recollection room. I think if you play Part 1, you can't access the recollection room until you reach the very very end of the entire update, whereas in Part 2, the Administrator's role gives some asinine easy excuse to have better access to the recollection room. It's also a better way to explain how the heck you see Asuna POV scenes without arousing suspicion, since Part 1 you can for whatever reason check into Asuna's house, but also do nothing about what you see.
There are problems with the administrator's role in the story by just making certain things too easy for Inoda, but whether the Administrator was there or not, it's just a physical representation that Fujino (the god of this game) is going to always work towards making sure Inoda will ultimately steal Asuna and beat Kirito.
Also your opinion on the cumdump fmc, and cucked bf/husband, that is more or less what's going to happen. It is an NTR, and we're not exactly here to praise Fujino for novelesque writing. I think what people end up liking a lot from Fujino's earlier games was that the CGs he used were hot, and also that they let you explore and have that sense of mystery. It's more like a CG hunt or Voyeurism like game/experience. Most people don't insert themselves as the cuck, and are here along for the ride wanting to see things from both the mysterious side and also seeing all sides.